Confusing thoughts and speech: source monitoring and psychosis

www.elsevier.com/locate/psychres

Psychiatry Research 1

Confusing thoughts and speech: source monitoring and psychosis

Cecile Henqueta,*, Lydia Krabbendama, Jorg Dautzenberg,

Jelle Jollesa, Harald Merckelbachb

aDepartment of Psychiatry and Neuropsychology, South Limburg Mental Health Research and Teaching Network, EURON,

Maastricht University, P.O. Box 616, 6200 MD Maastricht, The NetherlandsbDepartment of Experimental Psychology, Maastricht University, P.O. Box 616, 6200 MD Maastricht, The Netherlands

Received 31 July 2003; received in revised form 26 July 2004; accepted 11 August 2004

Abstract

To explore the idea that deficits in source monitoring may underlie positive symptoms of schizophrenia, the current study

compared schizophrenic patients’ performance (n=15) on an internal source-monitoring task with that of normal controls

(n=15). On the basis of a source-monitoring task in which participants had to recall whether they had verbalized answers or

merely thought about these answers, overall source monitoring performance, discrimination index, and response bias were

calculated. In addition, participants completed cognitive tests and symptomatology questionnaires. Relative to controls, patients

had significantly more difficulties with monitoring their own actions and showed a tendency towards misclassifying imagined

thoughts as verbalized thoughts. Source-monitoring performance was related to selective attention, but not to other cognitive

domains. No relationship was found between source monitoring and symptomatology. Failures in internal source monitoring are

a prominent feature of schizophrenia, and our results suggest that they form a more enduring characteristic of this disorder than

has previously been assumed.

D 2004 Elsevier Ireland Ltd. All rights reserved.

Keywords: Schizophrenia; Positive symptoms; Psychosis-related traits; Self-monitoring; Neuropsychological deficits

1. Introduction

Source monitoring refers to cognitive processes

involved in determining the source of memory

information (Johnson et al., 1993). The following

0165-1781/$ - see front matter D 2004 Elsevier Ireland Ltd. All rights re

doi:10.1016/j.psychres.2004.08.009

* Corresponding author. Tel.: +31 43 3299773; fax: +31 43

3299708.

E-mail address: [email protected] (C. Henquet).

three source-monitoring situations can be distin-

guished: (a) discriminating between internally gen-

erated information (e.g., fantasies) and memories of

externally derived information, a process that is

usually termed reality monitoring (Johnson and Raye,

1981); (b) discriminating between two or more

external sources (e.g., television versus a good friend);

and (c) discriminating between two internal sources

(e.g., fantasies versus dreams), a process that is often

referred to as self-monitoring (Johnson et al., 1993).

33 (2005) 57–63

served.

C. Henquet et al. / Psychiatry Research 133 (2005) 57–6358

Transient source-monitoring errors are common in

everyday social situations. However, psychotic

experiences have been hypothesized to originate

from a fundamentally disturbed source monitoring.

Thus, several authors have argued that a specific

source-monitoring impairment may underlie certain

positive psychotic symptoms (Heilbrun, 1980; Hoff-

man, 1986; Bentall, 1990). For example, according

to Frith’s model of psychosis (Frith and Done,

1989; Frith, 1992), symptoms of alien control and

certain hallucinations arise from difficulties with

monitoring one’s own willed intentions, actions, and

thoughts, whereas other symptoms (e.g., paranoid

delusions) are due to difficulties in monitoring the

intentions of others. A number of source-monitoring

studies have shown that during the acute phase of

schizophrenia, patients find it difficult to discrim-

inate between self-generated items and items

generated by the researcher (Keefe et al., 1999;

Brebion et al., 2000). The majority of these studies

suggest that an external attribution bias underlies

reality-monitoring failures exhibited by schizo-

phrenic patients (Harvey, 1985; Keefe et al.,

1999; see also Franck et al., 2000). In this line

of reasoning, positive symptoms (e.g., hallucinations

and certain delusions) originate from a tendency to

attribute self-generated information to an external

source (Slade and Bentall, 1988).

Many previous studies on schizophrenic patients’

source-monitoring abilities relied on tasks that were

highly artificial, in the sense of being far removed

from everyday situations. A typical approach involves

presenting the patient with examples of a certain

category and asking him/her to generate other

examples. Subsequently, the patient has to differ-

entiate between these two sources of information (e.g.,

Brebion et al., 2000). Although this type of design has

provided important insights, a potential limitation is

that its results may be difficult to generalize to real-

life source-monitoring tasks (Parks, 1997). With this

in mind, the present study relied on a source-

monitoring task involving the common situation in

which one tries to remember whether one has actually

said or only thought something (Parks, 1997). Thus,

we investigated whether schizophrenic patients make

more mistakes on such an everyday source-monitor-

ing task than matched normal controls, and if so,

whether these mistakes specifically take the form of

falsely identifying internal thoughts as verbalized

thoughts.

There is still controversy regarding the precise

relationship between source-monitoring performance

and other cognitive functions (Brebion et al., 1996;

Seal et al., 1997; Stirling et al., 1998). Seal et al.

(1997) opined that performance on self-monitoring

tasks is confounded by factors such as verbal

intelligence, whereas the study by Stirling and

colleagues indicated that self-monitoring perform-

ance is unrelated to general cognitive functioning

(Stirling et al., 1998). Interestingly, Brebion et al.

(1996) found schizophrenic patients’ source-moni-

toring performance to be related to selective

attention, but not to memory capacity. We addressed

this issue by examining the links between source-

monitoring scores and performance in other cogni-

tive domains, notably general intelligence, attention,

and memory.

2. Method

2.1. Subjects

Participants were 15 patients with schizophrenia

and 15 healthy controls. Patients were recruited

through clinical and ambulatory facilities of psychi-

atric hospital Vijverdal, Maastricht, the Netherlands.

Diagnoses were made by patients’ psychiatrists

based on DSM-IV criteria (American Psychiatric

Association, 1994). Mean age of the patient group

(14 men; 1 woman) was 26.7 years (S.D.=6.4).

Their average level of education measured on an 8-

point scale, ranging from primary school to univer-

sity degree, was 3.7 (S.D.=1.4). Average scores on

the Positive and Negative Syndrome Scale (PANSS;

Kay et al., 1986) were 9.6 (S.D.=3.1) for the

positive scale and 10.0 (S.D.=2.6) for the negative

scale, indicating low levels of acute symptoms in

the patient group. Eight patients received antipsy-

chotic medication, with four of them using conven-

tional neuroleptics and four receiving atypical

neuroleptic drugs.

Control participants were recruited from the

general population through random mailings in the

local area and through the staff in the same

psychiatric hospital. An attempt was made to match

C. Henquet et al. / Psychiatry Research 133 (2005) 57–63 59

controls with patients on age. Controls were only

included if they had an absence of a lifetime history

of any psychiatric disorder. None of them used

psychotropic medication. The mean age of the

control group (11 men; 4 women) was 26.6 years

(S.D.=8.4), while the average level of education was

5.3 (S.D.=1.0). Patient and control groups did not

differ with regard to age [t(26)b1.0, P=0.98] or

gender distribution [x2(1)=2.16, P=0.14]. However,

patients had a significantly lower level of education

than controls [t(26)=3.79, Pb0.01].

For both patients and controls, the following

exclusion criteria were used: (i) head trauma (with

loss of consciousness), (ii) alcohol abuse (more than 5

units per day), and (iii) weekly use of drugs.

Participants were paid for their participation, and

written informed consent was obtained from all

participants.

2.2. Materials and procedure

The source-monitoring task was derived from a

series of studies by Parks (1997) and addressed

participants’ ability to discriminate thoughts from

actually verbalized thoughts. More specifically, par-

ticipants had to indicate whether they had verbalized

answers to earlier presented questions or only

imagined they did. Materials consisted of 24 non-

intrusive questions concerning personal history (e.g.,

bWhen were you born?Q) and opinion (e.g., bWhat

food do you like?Q). Questions were presented on a

computer screen, using a computer program specifi-

cally developed for this purpose (Dautzenberg and

Henquet, 2000).

The source-monitoring task involved 16 trials. On

half of the trials, single questions were presented. On

the other half, questions were presented in pairs, with

one question being located at the top half of the

computer screen and the other being located at the

bottom half of the screen. Questions were presented,

after which a white screen was shown for 3 s.

Participants had to prepare an answer to the presented

questions. On single question trials, the word

banswerQ appeared shortly after presentation of the

question. On dual question trials, either the words

banswer topQ or banswer bottomQ appeared. Thus,

here participants had to prepare an answer to both

questions, but they verbalized only one answer. This

resulted in verbalizing answers to 16 questions, while

8 answers were covertly prepared but never verbal-

ized. Single questions and pairs were presented in a

quasi-random order, and two counterbalanced ver-

sions were used. Participants were randomly allo-

cated to one of the two versions. An examiner was

present to monitor whether participants actually

verbalized the answers. All participants were capable

of answering the questions, which makes clear that

the questions were simple and direct. Participants

were instructed to press a button as soon as they had

prepared an answer for the questions. Preparation

time varied between participants but never took

longer than 7 s. Given this constellation, we have

every reason to believe that participants actually did

prepare answers during the preparation phase of two-

question trials, as opposed to merely remembering

the questions. Following the presentation of the

questions and a filler task (which took about 5

min), participants were given a surprise recognition

task. In this task, participants saw original questions,

each paired with a new question of the same content

and form. For example, the old item bWhen were you

born?Q was presented along with the new item

bWhere were you born?Q Participants were asked to

identify for each of the 24 pairs of old and new items

the question they had seen before (i.e., the memory

aspect of the task). Further, they had to indicate

whether they verbalized answers to the boldQ items or

only thought about an answer (i.e., the source-

monitoring aspect of the task).

Neuropsychological assessment focused on intelli-

gence and selective attention. Overall intellectual

functioning was measured by three subtests of the

Groningen Intelligence Test (GIT; Luteijn and van der

Ploeg, 1983). The Stroop Color-Word test (Stroop,

1935) was used to tap selective attention (Houx et al.,

1991). This test involves three cards displaying color

names, colored patches, and color names printed in

inconsistent ink colors (cards I–III, respectively). The

time needed to complete card III is largely determined

by the ability to ignore irrelevant but salient verbal

color names, so as to color name the ink of the words.

To obtain a measure of selective attention, Stroop

response latencies were transformed into a Stroop

interference score. The Schizotypal Personality Scale-

A (STA; Claridge and Broks, 1984) was administered

to measure schizotypal traits. Hallucinations, delu-

Table 1

Mean age, level of education, intelligence, and symptomatology of

patients and control participants (standard deviations are given

between parentheses)

Patients

(n=15)

Controls

(n=15)

t P

Age 26.7 (6.4) 26.6 (8.4) �0.02 0.98

Level of education 3.7 (1.4) 5.3 (1.0) 3.79 0.01

GIT IQa 96.1 (10.2) 113.5 (13.2) 4.02 0.00

Stroop interference 72.53 (30.0) 61.87 (15.4) �1.23 0.23

STAb 13.8 (11.5) 6.5 (4.27) �2.21 0.04

a Intelligence quotient based on the Groningen Intelligence Test

(GIT).b Schizotypal Personality Assessment.

Table 2

Mean performance scores on the source-monitoring task of patients

and control participants (standard deviations are given between

parentheses)

Patients

(n=15)

m (S.D.)

Controls

(n=15)

m (S.D.)

t P

Total scorea 0.79 (0.08) 0.88 (0.09) 2.84 0.01

Discrimination

indexb0.50 (0.20) 0.69 (0.16) 2.94 0.01

Response biasc 0.53 (0.27) 0.53 (0.21) 0.02 0.99

False-alarm rated 0.29 (0.25) 0.16 (0.11) �1.87 0.07

Missing ratee 0.20 (0.12) 0.14 (0.11) �1.35 0.19

Memoryf 0.95 (0.07) 1.00 (0.00) 2.92 0.01

a Proportion of total correct score.b Measure of accuracy.c Measure of biased responding.d Proportion of false positives.e Proportion of false negatives.f Proportion correct recognition of old items.

C. Henquet et al. / Psychiatry Research 133 (2005) 57–6360

sions, and thought disorders were rated with the

PANSS (Kay et al., 1986).

2.3. Data analyses

Data analysis was carried out using SPSS for

Windows Version 10.0. Six source-monitoring indi-

ces were derived. First, a total score of correct

source-monitoring responses was obtained by sum-

ming the number of old items that participants

correctly classified as verbalized or covertly pre-

pared items. Second, the memory score was

calculated by summing the number of correctly

identified old items. To correct for misses, source-

monitoring responses were transformed into propor-

tions of the total number of the 16 questions minus

missed items.

Third, following the Two-High Threshold theory

(Corwin, 1994), we calculated false-alarm rates (i.e.,

erroneous claims of verbalized answers) and missing

rates (i.e., failures to identify verbalized answers). In

keeping with the work of Brebion et al. (1997), we

calculated a discrimination index and a response bias

index, as measures of accurate and biased discrim-

ination between internal and external thoughts,

respectively. In doing so, we took the number of

erroneous answers into account. Thus, the discrim-

ination index was defined as: (number of hits+0.5/

number of targets+1)�(number of false alarms+0.5/

number of distractors+1). Response bias was defined

as: (number of false alarms+0.5/number of distrac-

tors+1)/(1�discrimination index). Note that the

source-monitoring task consisted of 16 targets (ver-

balized answers) and 8 distractors (covertly prepared

answers). Measures were calculated into group means

and compared between groups.

Group differences in source-monitoring perform-

ance, memory capacity, IQ, selective attention, and

symptomatic measures were evaluated with Student

t-tests. In addition, for the combined groups, Pearson

correlations were calculated between the source-

monitoring discrimination index and cognitive and

symptomatic measures. Further, a Pearson correlation

was calculated between source-monitoring perform-

ance and memory score. Multiple regression analysis

was conducted with the discrimination index as the

dependent variable and IQ, level of education,

Stroop interference, and memory as independent

variables.

3. Results

Basic psychometric information about the two

groups is summarized in Table 1. As can be seen,

patients had a lower educational level, lower IQ, but

higher scores on STA than controls. Table 2 shows

source-monitoring indices. Patients had fewer correct

responses (i.e., correct identifications of verbalized

versus internally prepared items) than controls:

t(28)=2.84, Pb0.01. Groups also differed with regard

to a number of Two-High Threshold theory parame-

ters. Thus, relative to controls, patients were signifi-

C. Henquet et al. / Psychiatry Research 133 (2005) 57–63 61

cantly worse at discriminating between targets and

distractors, taking into account the number of errors

they made [i.e., patients scored lower on the discrim-

ination index than controls: t(28)=2.94, Pb0.01].

Furthermore, relative to controls, patients tended to

misclassify imagined thoughts as verbalized answers

[t(28)=�1.87, P=0.07]. However, when overall per-

formance accuracy was taken into account, no

response bias was evident. There were no group

differences with regard to the opposite type of failure

(i.e., misclassifying a verbalized response as an

imagined response). However, patients performed

worse than controls on the memory aspect of the

source-monitoring task [t(28)=2.92, Pb0.01].

Table 3 shows correlations between the discrim-

ination index derived from the source-monitoring

task, cognitive performance indices, and symptoma-

tology scores for the full sample. The discrimination

index correlated significantly with IQ, selective

attention, and memory capacity. The correlation

between source-monitoring performance and memory

score remained non-significant (r=0.34, P=0.07).

Multiple regression analysis in which IQ, selective

attention, level of education, and memory scores were

entered together showed that only selective attention

and IQ contributed significantly to the source-mon-

itoring discrimination index (R2=0.45). Alone, selec-

tive attention accounted for only 52% of the variance

in the discrimination index. Analyses were repeated to

compare medicated versus unmedicated patients.

Medicated patients showed better performance on

source-monitoring total score [t(13)=2.22, Pb0.05]

and had higher scores on the discrimination index

[t(10)=3.33, Pb0.01]. However, multiple regression

Table 3

Pearson product-moment correlations between source-monitoring

discrimination index, level of education, cognitive performance, and

symptomatology

Discrimination index

r P

Level of education 0.25 0.19

IQ (GIT) 0.44 0.02

Stroop interference �0.52 0.00

Memory 0.37 0.04

STA �0.14 0.49

PANSSa �0.06 0.84

a Positive and Negative Syndrome Scale.

analysis in which IQ, selective attention, and use of

medication were entered together showed that use of

medication did not contribute significantly to the

source-monitoring discrimination index (R2=0.44).

No differences between medicated and unmediated

patients were observed in response bias or memory

capacity. Symptomatology as measured with the STA

and PANSS did not correlate significantly with total

scores on the source-monitoring task (all r’sb0.14; all

P’sN0.49).

4. Discussion

This study demonstrates different patterns of

source-monitoring performance in patients with schiz-

ophrenia and normal controls. Thus, compared with

normal control subjects, patients showed more diffi-

culties in discriminating between covert and

expressed thoughts, a finding that is in accordance

with previous research (e.g., Brebion et al., 1997). We

also found some tentative evidence to suggest that

relative to controls, patients exhibited a stronger

tendency to identify an item as verbalized, when in

fact it was only covertly prepared. However, this

difference was statistically imprecise, which may have

to do with the small sample size. Note that this

tendency is well in line with other studies document-

ing schizophrenic patients’ bias to attribute internal

stimuli to external sources (Brebion et al., 1998, 2000;

Keefe et al., 1999; Franck et al., 2000). Interestingly,

we found no group differences in the opposite

tendency, i.e., the tendency to falsely attribute

verbalized items to imagined thoughts. However,

group differences in source-monitoring errors were

not reflected in response-bias elevations (which

include overall source-monitoring accuracy). This

might indicate that our finding of higher false-alarm

level in patients reflects overall inaccuracy of source-

monitoring performance instead of response bias. On

the other hand, the design of the task might have

elicited floor effects in response bias.

Regression analysis showed that selective attention

as indexed by the Stroop task, more than general

memory capacities, statistically predicts source-mon-

itoring performance. Interestingly, these findings

replicate results reported by Brebion et al. (1996).

Perhaps, deficits in selective attention lead to dis-

C. Henquet et al. / Psychiatry Research 133 (2005) 57–6362

turbances in the primary encoding process of infor-

mation, which could then result in decreased quality

of source monitoring. The fact that IQ also contrib-

uted significantly to source-monitoring performance is

a finding that has been described earlier in schizo-

phrenia research (Seal et al., 1997), although other

studies did not describe such a relationship between

source-monitoring performance and overall cognitive

functioning (Stirling et al., 1998).

Although there were differences in source-mon-

itoring performance between medicated and unmedi-

cated patients, regression analyses showed that

medication was not a pure independent predictor for

source-monitoring performance, which is well in line

with the general notion that memory deficits in

schizophrenia patients have little or nothing to do

with anti-psychotic medication (Aleman et al., 1999).

There is some debate as to whether positive

symptoms are specifically linked to source-monitoring

deficits. Whereas Franck et al. (2000) and Brebion et

al. (2000) found evidence for such a specific link,

Keefe et al. (1999) found schizophrenic patients’

tendency to misclassify imagined words as externally

perceived not related to their positive symptoms. The

current study concurs with that of Keefe et al. (1999)

in that we were also unable to find a significant

correlation between psychosis-related traits or symp-

tomatology, on the one hand, and source-monitoring

performance, on the other. However, a methodological

restriction might underlie this null finding. Because of

our limited sample size, STA scores lacked sufficient

variation, with especially low rates of psychosis-

related traits in the control group. A larger sample

with more variation among trait scores might reveal a

relationship between psychosis-related traits and

source monitoring more clearly.

It has generally been assumed that failures in

source-monitoring performance reflect a state-depend-

ent deficit related to the positive symptoms of

schizophrenia (Frith and Done, 1989; Slade and

Bentall, 1988; Stirling et al., 1998; Brebion et al.,

2000), as opposed to other cognitive deficits which

seem to persist during clinical remission (Nopoulos et

al., 1994; Cantor Graae et al., 1995). Yet, the fact that

straightforward failures in source monitoring were

identified in patients with few acute positive symp-

toms contradicts the alleged state-dependent character

of these deficits.

As argued in the Section 1, many laboratory

experiments on source monitoring expose participants

to situations that rarely occur in everyday life. We feel

that the procedure used in this study has better

ecological validity because it focuses on an everyday

life situation: dDid I just answer your question, or do I

only think I did?T Our results show that patients with

schizophrenia have great difficulty with this task.

In conclusion, internal source monitoring is

impaired in patients with schizophrenia. The defec-

tive memory performance generally found in these

patients does not seem to underlie this impairment,

but selective attention and general intelligence do

contribute to variation in source-monitoring per-

formance. A relation with the severity of positive

symptoms could not be found in this study,

possibly due to limited variation in symptoms in

the current sample. Yet, failures in internal source

monitoring are present in psychotic disorders

independent of positive psychotic symptoms, indi-

cating that these deficits are at least to some extent

part of an enduring cognitive vulnerability in

schizophrenia.

Acknowledgment

The authors thank Joke Conings, MSc for her help

in collecting and analyzing the data.

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